Egyptian experience of reliability of 4T's score in diagnosis of heparin induced thrombocytopenia syndrome

Abstract

To evaluate the utility of the 4Ts clinical scoring system as a pretest probability method for detection of heparin-induced thrombocytopenia (HIT). Medical and surgical inpatients and outpatients at Kasr El Eini hospital. This single-centre series of 50 HIT testing referrals assessed combination of clinical score (thrombocytopenia, timing, thrombosis, other causes of thrombocytopenia not evident; 4T's), Heparin platelet factor 4 (H-PF4) rapid particle gel immunoassay (PaGIA) and 14C serotonin release assay (SRA) to develop a practical and well tolerated diagnostic strategy for HIT. Sixteen patients (32%) had a low 4T's score, 26 (52%) had an intermediate score and only eight (16%) had a high score. A positive H-PF4 by PaGIA was seen in seven patients (14%). As might be anticipated, the likelihood of obtaining a positive H-PF4 by PaGIA increased with an increasing clinical score, with positive H-PF4 by PaGIA results in low, intermediate and high scoring patients of 6.25, 7.7 and 50%, respectively. The positive predictive value of a positive PaGIA was 92%. The negative predictive value was 100%. Five patients (10%) in our cohort had a positive SRA. All patients with a positive SRA were included in the intermediate (two of 26 patients, 7.7%) or high (three of eight patients, 37.5%) score groups. The negative predictive value of a low 4T's score was 100%, effectively ruling out HIT. A low 4Ts score supports low probability of HIT based on the results of the PaGIA and SRA. Overall, the interrater reliability of the scoring system was fair.